1. Gas-guzzling grow ops

Growing cannabis indoors produces approximately 15-million metric tons of carbon emissions each year. That's the equivalent of three-million average American cars. Cultivating one kilogram of processed marijuana produces roughly the same amount of emissions as driving across America five times.

The main polluters are illegal grow operations, which tend to use diesel and gasoline generators because using the grid means generating electric bills that would tip off authorities about the illegal operation. Staying off the grid is good for illegal growers, but it's a nightmare for the environment.

2. Cleaning up the grid

Getting illegal growers on the grid would be a great start. But more work has to be done to make the industry ecologically sound.

Approximately 67 percent of electricity in the U.S. is generated by burning fossil fuels. So the electricity used by indoor growers would still generate pollutants that lead to climate change. Indeed, indoor growers require eight times as much power per square foot of space as a commercial building. So switching from fossil fuels to electricity produced by fossil fuels would really only reduce the industry's giant carbon footprint by a few shoe sizes.

Unfortunately, there's no way to make the world stop using fossil fuels overnight. Warren notes,

"Even in the face of the devastating impacts of climate change, it is simply not feasible (or desirable) to immediately remove all fossil fuels as a source of energy. The world economy would certainly collapse and many people would suffer immediate physical and financial harm."

However, governments can prevent fossil-fuel consumption from increasing by adding special regulations to new industries. Warren says,

"States and local governments should take the first steps toward eliminating fossil fuels as energy sources... by mandating that new industries, such as the marijuana industry, ultimately use carbon-free energy sources as a condition of licensing."

Since legislators essentially have a clean slate for regulating the cannabis industry, they have a unique opportunity to make the legal cannabis industry environmentally friendly on day one.

3. Federal legalization still needed

Legalization would also open up opportunities for growers to consult with energy providers in order to strategize ways to use energy more efficiently.

For instance, energy providers could coordinate with growers to deal with peak hours of energy consumption. During that time, energy grids tend to run almost entirely on fossil fuels. So the cannabis industry could reduce its carbon footprint by managing its consumption of electricity around non-peak times.

State legalization would be a start to this dialog, but Warren warns that some utility companies might be hesitant to work with an industry that is federally prohibited. So the nationwide repeal of prohibition would be needed for the cannabis industry to take a giant leap toward making marijuana ecologically sound.

4. Regulating a green industry

Many states rely on fossil fuels for the bulk of their electricity, so even working around peak hours won't do enough to reduce the cannabis industry's carbon footprint in some areas. Those states would have to develop renewable sources such as solar, wind and hydropower in order to make cannabis a green industry. It's a great idea, but developing those sources is costly.

To fix this problem, Warren recommends looking into a carbon fee for the industry that would fund the state's development of climate-friendly energy resources. But she cautions against imposing a flat rate because that might make businesses complacent about paying the fee instead of finding ways to make the industry environmentally friendly. Instead, she suggests increasing the rate over time to incentivize the industry to find green solutions to their energy consumption.

5. Keeping green from going back to black

However, Warren urges states not to impose regulations that are too strict or costly. Doing so might inadvertently incentivize people to go back to the black market, recreating all the environmental hazards and climate-unfriendly practices that states hoped to eliminate through legalization.

Including some fees and regulations to reduce the industry's impact on climate change would be a good start. But states shouldn't expect the cannabis industry to pick up the tab for overhauling their energy sectors.

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